High frequency switch circuit

ABSTRACT

This invention relates to a high frequency switch circuit including a plurality of high frequency terminals ( 101, 102, 103 ) which input/output a high frequency signal, and a plurality of high frequency semiconductor switch sections ( 121, 122 ) which switch between these high frequency terminals. The plurality of high frequency semiconductor switch sections are isolated from each other in a DC state by a DC potential isolating section ( 131 ), and a DC potential opposite in level to a DC potential applied to a switching signal terminal ( 111, 112 ) arranged on the control side of each high frequency semiconductor switch section is applied to both or at least one of the input side and output side of each high frequency semiconductor switch section.

TECHNICAL FIELD

[0001] The present invention relates to a high frequency switch circuitused in high frequency communication of a portable cellular phone setand the like.

BACKGROUND ART

[0002]FIG. 1 is a circuit diagram showing the first prior art of a highfrequency switch circuit. The first prior art will be explained withreference to FIG. 1.

[0003] The first prior art concerns an SPDT circuit (Single Pole DoubleTransfer) disclosed in Japanese Unexamined Patent Publication No.8-139014. The drains and sources of field effect transistors 1 to 5 arecascade-connected between high frequency terminals 101 and 102. Thedrains and sources of field effect transistors 6 to 10 arecascade-connected between the high frequency terminal 101 and a highfrequency terminal 103. The gate electrodes of the field effecttransistors 1 to 10 are connected to resistance elements 51 to 60. Theresistance elements 51 to 55 connected to the gate electrodes of thefield effect transistors 1 to 5 are connected to a switching signalterminal 111. The resistance elements 56 to 60 connected to the gateelectrodes of the field effect transistors 6 to 10 are connected to aswitching signal terminal 112.

[0004] Voltages at opposite levels are input to the switching signalterminals 111 and 112. When high level is input to the switching signalterminal 111 and low level is input to the switching signal terminal112, the field effect transistors 1 to 5 are turned on, the field effecttransistors 6 to 10 are turned off, and the high frequency terminals 101and 102 are rendered conductive. When low level is input to theswitching signal terminal 111 and high level is input to the switchingsignal terminal 112, the field effect transistors 1 to 5 are turned off,the field effect transistors 6 to 10 are turned on, and the highfrequency terminals 101 and 103 are rendered conductive.

[0005]FIG. 2 is a circuit diagram showing the second prior art of a highfrequency switch circuit. The second prior art will be explained withreference to FIG. 2.

[0006] The second prior art concerns an SPDT circuit disclosed inJapanese Unexamined Patent Publication No. 8-213893. High frequencyterminals 101 and 102 are connected by a field effect transistor 1, andthe high frequency terminal 101 and a high frequency terminal 103 areconnected by a field effect transistor 2. The high frequency terminal102 is grounded via the drain-source path of a field effect transistor 3and a capacitive element 71. The high frequency terminal 103 is groundedvia the drain-source path of a field effect transistor 4 and acapacitive element 72. The gate electrodes of the field effecttransistors 1 to 4 are connected to resistance elements 51 to 54,respectively. The resistance element 51 connected to the gate electrodeof the field effect transistor 1 and the resistance element 54 connectedto the gate electrode of the field effect transistor 4 are connected toa switching signal terminal 111. The resistance element 52 connected tothe gate electrode of the field effect transistor 2 and the resistanceelement 53 connected to the gate electrode of the field effecttransistor 3 are connected to a switching signal terminal 112. The highfrequency terminals 101 to 103 and the source electrodes of the fieldeffect transistors 3 and 4 are connected to an external power supply 300via resistance elements 55 to 59.

[0007] Voltages at opposite levels are input to the switching signalterminals 111 and 112. The high frequency terminals 101 to 103 and thesource electrodes of the field effect transistors 3 and 4 receive thepotential of the external power supply 300 via the resistance elements55 to 59. When high level is input to the switching signal terminal 111and low level is input to the switching signal terminal 112, the fieldeffect transistors 1 and 4 are turned on, the field effect transistors 2and 3 are turned off, and the high frequency terminals 101 and 102 arerendered conductive. When low level is input to the switching signalterminal 111 and high level is input to the switching signal terminal112, the field effect transistors 1 and 4 are turned off, the fieldeffect transistors 2 and 3 are turned on, and the high frequencyterminals 101 and 103 are rendered conductive.

[0008] The SPDT circuit is incorporated in, e.g., a portable cellularphone set, and functions as a high frequency transmission/receptionsignal switch. The field effect transistor used in the high frequencyswitch circuit is, e.g., a depletion n-channel GaAs MESFET, and isturned on at 0[V] and off at −3[V].

[0009] The conventional high frequency switch circuit suffers thefollowing problems.

[0010] In the first prior art, no potential is externally applied to ahigh frequency terminal, and high frequency terminals at the twoterminals (drain and source sides) of an ON field effect transistor areset to almost the same potential as high level. The potential differencebetween the gate and the source becomes almost 0[V], and the ONresistance cannot be sufficiently reduced. That is, the transmissionloss increases.

[0011] In the second prior art, a potential is externally applied to ahigh frequency terminal, and a gate-source potential Vgs can bepositively increased depending on an application potential VC. The ONresistance can be reduced, and as a result, the transmission loss can bereduced. A maximum handling power Pmax which can be handled by a circuitconstituted by cascade-connecting n field effect transistors is given by

Pmax=2{n(VC−VL+VT)}2/Zo

[0012] (where VL is low level, VT is the threshold voltage of the fieldeffect transistor, and Zo is the evaluation system impedance in theswitch circuit.)

[0013] The difference between low level (VL) and VC becomes small,decreasing handling power. To increase handling power, the number ofcascade-connected field effect transistors must be increased. Anexternal power supply is undesirably required.

[0014] In other words, in the conventional high frequency switchcircuit, signal transmission paths are DC-connected. If Vgs of an ONswitch is positively increased to reduce the ON resistance, handlingpower decreases in an OFF switch. If Vgs of an OFF switch is negativelyincreased to increase handling power, the ON resistance of an ON switchincreases.

DISCLOSURE OF INVENTION

[0015] The present invention has been made in consideration of the abovesituation in the prior art, and has as its object to provide a highfrequency switch circuit which meets both low transmission loss and highhandling power.

[0016] To achieve the above object, according to the first aspect of thepresent invention, there is provided a high frequency switch circuitcharacterized by comprising a plurality of high frequency terminalswhich input/output a high frequency signal, and a plurality of highfrequency semiconductor switch sections which switch between the highfrequency terminals, wherein the plurality of high frequencysemiconductor switch sections are isolated from each other in a DCstate, and a DC potential opposite in level to a DC potential applied toa control side is applied to at least one of an input side and an outputside of each of the plurality of high frequency semiconductor switchsections.

[0017] The “high frequency semiconductor switch section” is mainlycomprised of a semiconductor switch element such as a field effecttransistor or bipolar transistor, and will be referred to as a “highfrequency semiconductor switch section” hereinafter. The “DC potentialopposite in level to a DC potential applied to the control side of thehigh frequency semiconductor switch section” means a DC potential foropening the high frequency semiconductor switch section when a DCpotential for closing the high frequency semiconductor switch section isapplied to the control side, and a DC potential for closing the highfrequency semiconductor switch section when a DC potential for openingthe high frequency semiconductor switch section is applied to thecontrol side.

[0018] The high frequency semiconductor switch sections are isolatedfrom each other in the DC state. The input side or output side of eachhigh frequency semiconductor switch section receives a DC potentialopposite in level to a DC potential applied to the control side. A highfrequency semiconductor switch section which is closed upon applicationof a high-level potential to the control side will be explained. Whenthe high frequency semiconductor switch section is closed uponapplication of a high-level potential to the control side, a low-levelpotential is applied to the input side or output side. The controlvoltage becomes much higher than the input/output voltage, and the ONtransmission resistance value decreases. When the high frequencysemiconductor switch section is opened upon application of a low-levelpotential to the control side, a high-level potential is applied to theinput side or output side. The control voltage becomes much lower thanthe input voltage, and the OFF handling power increases. As for a highfrequency semiconductor switch section which is closed upon applicationof a low-level potential, the level of the DC potential in the abovedescription is reversed.

[0019] According to the second aspect of the present invention, there isprovided a high frequency switch circuit characterized in that theplurality of high frequency semiconductor switch sections in the firstaspect include field effect transistors having drain electrodes andsource electrodes which are connected between the high frequencyterminals, the plurality of high frequency semiconductor switch sectionsare isolated from each other by capacitive elements, and a DC potentialopposite in level to a DC potential applied to a gate electrode isapplied to at least one of the drain electrode and the source electrode.

[0020] According to the third aspect of the present invention, there isprovided a high frequency switch circuit characterized in that theplurality of high frequency semiconductor switch sections in the firstaspect include a plurality of field effect transistors having drainelectrodes and source electrodes which are series-connected between thehigh frequency terminals, the plurality of high frequency semiconductorswitch sections are isolated from each other by capacitive elements, anda DC potential opposite in level to a DC potential applied to gateelectrodes is applied to at least either of the drain electrodes and thesource electrodes at both sides of the plurality of field effecttransistors.

[0021] According to the fourth aspect of the present invention, there isprovided a high frequency switch circuit comprising first to third highfrequency terminals which input/output a high frequency signal, a firsthigh frequency semiconductor switch section which switches between thethird high frequency terminal and the first high frequency terminal, asecond high frequency semiconductor switch section which switchesbetween the third high frequency terminal and the second high frequencyterminal, a first switching signal terminal which controls switchingoperation of the first high frequency semiconductor switch section, asecond switching signal terminal which controls switching operation ofthe second high frequency semiconductor switch section, a DC potentialisolating section which is connected between the third high frequencyterminal and the first and second high frequency semiconductor switchsections, and isolates the first high frequency semiconductor switchsection and the second high frequency semiconductor switch section in aDC state, a first potential transmission section which is connectedbetween the second switching signal terminal and the first highfrequency terminal, and applies to the first high frequency terminal aDC potential applied to the second switching signal terminal, and asecond potential transmission section which is connected between thefirst switching signal terminal and the second high frequency terminal,and applies to the second high frequency terminal a DC potential appliedto the first switching signal terminal.

[0022] According to the fifth aspect of the present invention, there isprovided a high frequency switch circuit comprising first to fourth highfrequency terminals which input/output a high frequency signal, a firsthigh frequency semiconductor switch section which switches between thefirst high frequency terminal and the second high frequency terminal, asecond high frequency semiconductor switch section which switchesbetween the second high frequency terminal and the third high frequencyterminal, a third high frequency semiconductor switch section whichswitches between the third high frequency terminal and the fourth highfrequency terminal, a fourth high frequency semiconductor switch sectionwhich switches between the fourth high frequency terminal and the firsthigh frequency terminal, a first switching signal terminal whichcontrols switching operation of the first and third high frequencysemiconductor switch sections, a second switching signal terminal whichcontrols switching operation of the second and fourth high frequencysemiconductor switch sections, a first DC potential isolating sectionwhich is connected between the first high frequency terminal and thefourth and first high frequency semiconductor switch sections, andisolates the fourth high frequency semiconductor switch section and thefirst high frequency semiconductor switch section in a DC state, asecond DC potential isolating section which is connected between thesecond high frequency terminal and the first and second high frequencysemiconductor switch sections, and isolates the first high frequencysemiconductor switch section and the second high frequency semiconductorswitch section in the DC state, a third DC potential isolating sectionwhich is connected between the third high frequency terminal and thesecond and third high frequency semiconductor switch sections, andisolates the second high frequency semiconductor switch section and thethird high frequency semiconductor switch section in the DC state, afourth DC potential isolating section which is connected between thefourth high frequency terminal and the third and fourth high frequencysemiconductor switch sections, and isolates the third high frequencysemiconductor switch section and the fourth high frequency semiconductorswitch section in the DC state, a first potential transmission sectionwhich is connected between the second switching signal terminal and atleast one of an input side and an output side of the first highfrequency semiconductor switch section, and applies to at least one ofthe input side and the output side a DC potential applied to the secondswitching signal terminal, a second potential transmission section whichis connected between the first switching signal terminal and at leastone of an input side and an output side of the second high frequencysemiconductor switch section, and applies to at least one of the inputside and the output side a DC potential applied to the first switchingsignal terminal, a third potential transmission section which isconnected between the second switching signal terminal and at least oneof an input side and an output side of the third high frequencysemiconductor switch section, and applies to at least one of the inputside and the output side a DC potential applied to the second switchingsignal terminal, and a fourth potential transmission section which isconnected between the first switching signal terminal and at least oneof an input side and an output side of the fourth high frequencysemiconductor switch section, and applies to at least one of the inputside and the output side a DC potential applied to the first switchingsignal terminal.

[0023] Two potential transmission sections are adopted for connection toboth the input side and output side of the high frequency semiconductorswitch section. One potential transmission section is adopted forconnection to either the input side or output side.

[0024] According to the sixth aspect of the present invention, the DCpotential isolating section in the fourth and fifth aspects includes acapacitive element which is connected between the high frequencyterminal connected to the DC potential isolating section and one highfrequency semiconductor switch section connected to the DC potentialisolating section, or between the high frequency terminal connected tothe DC potential isolating section and the other high frequencysemiconductor switch section connected to the DC potential isolatingsection.

[0025] According to the seventh aspect of the present invention, the DCpotential isolating section in the fourth to sixth aspects comprises afield effect transistor having a drain electrode and a source electrodewhich are connected between the high frequency terminal connected to theDC potential isolating section and one high frequency semiconductorswitch section connected to the DC potential isolating section, a fieldeffect transistor having a drain electrode and a source electrode whichare connected between the high frequency terminal connected to the DCpotential isolating section and the other high frequency semiconductorswitch section connected to the DC potential isolating section, and aresistance element which is connected between a gate electrode of eachfield effect transistor and the switching signal terminal.

[0026] According to the eighth aspect of the present invention, the DCpotential isolating section in the fourth to sixth aspects comprises afield effect transistor having a drain electrode and a source electrodewhich are connected between the high frequency terminal connected to theDC potential isolating section and one high frequency semiconductorswitch section connected to the DC potential isolating section, a fieldeffect transistor having a drain electrode and a source electrode whichare connected between the high frequency terminal connected to the DCpotential isolating section and the other high frequency semiconductorswitch section connected to the DC potential isolating section, aresistance element which is connected between a gate electrode of eachfield effect transistor and the switching signal terminal, and aresistance element which is connected between the drain electrode andthe source electrode of each field effect transistor.

[0027] According to the ninth aspect of the present invention, the highfrequency semiconductor switch section in the fourth to eighth aspectscomprises a field effect transistor having a drain electrode and asource electrode which are connected between the high frequencyterminals connected/disconnected by the high frequency semiconductorswitch section, a resistance element which is connected between a gateelectrode of the field effect transistor and the switching signalterminal for controlling the high frequency semiconductor switchsection, and a resistance element which is connected between the drainelectrode and the source electrode.

[0028] According to the tenth aspect of the present invention, the highfrequency semiconductor switch section in the fourth to eighth aspectscomprises a plurality of field effect transistors having drainelectrodes and source electrodes which are series-connected between thehigh frequency terminals connected/disconnected by the high frequencysemiconductor switch sections, a plurality of resistance elements whichare connected between gate electrodes of the field effect transistorsand the switching signal terminals for controlling the high frequencysemiconductor switch sections, and a plurality of resistance elementswhich are connected between the drain electrodes and the sourceelectrodes.

[0029] According to the eleventh aspect of the present invention, thepotential transmission section in the fourth to 10th aspects includes aresistance element.

[0030] According to the twelfth aspect of the present invention, thepotential transmission section in the fourth to 10th aspects includes aresistance element and an inductor element which are series-connected.

[0031] According to the thirteenth aspect of the present invention, thehigh frequency switch circuit in the first to 12th aspects is integratedin one semiconductor chip.

[0032] In other words, according to each aspect, the present inventioncomprises means for isolating in a DC state the potential of a highfrequency semiconductor switch section (ON side) on a path whichtransmits a signal and the potential of a high frequency semiconductorswitch section (OFF side) on a path which cuts off a signal, positivelyincreasing a gate-source potential on the ON side, and negativelyincreasing a gate-source potential on the OFF side. The high frequencysemiconductor switch section (ON side) on the path which transmits asignal and the high frequency semiconductor switch section (OFF side) onthe path which cuts off a signal are isolated in the DC state. On the ONside, a voltage at the switching signal terminal becomes higher thanvoltages on the input side and output side of the high frequencysemiconductor switch section, and their difference becomes large. As aresult, the ON transmission resistance value decreases, reducing thetransmission loss. On the OFF side, a voltage at the switching signalterminal becomes lower than voltages at the input terminal and outputterminal, and their difference becomes large, increasing the OFFhandling power. Since a DC potential is applied using a switching signalvoltage, no external power supply is required. In short, signaltransmission paths are isolated, and the voltage of a switching signalis exploited, positively increasing Vgs of an ON switch and negativelyincreasing Vgs of an OFF switch.

[0033] The high frequency switch circuit according to the presentinvention exhibits the following effects.

[0034] In the following description, the switching signal terminal is acontrol terminal, a voltage applied to the switching signal terminal isa control voltage, voltages on the input side and output side of thehigh frequency semiconductor switch section are an input/output voltage,“close” is “ON”, and “open” is “OFF” for a high frequency semiconductorswitch section which is closed upon application of a high potential tothe switching signal terminal and opened upon application of a lowpotential.

[0035] As the first effect, the control voltage is much higher than theinput/output voltage in a high frequency semiconductor switch section(ON side) on a path which transmits a high frequency signal, and the ONtransmission resistance value can be decreased to reduce thetransmission loss. This is because high frequency semiconductor switchsections are isolated from each other in the DC state, the input side oroutput side of the high frequency semiconductor switch section (ON side)is connected to the control terminal of the other high frequencysemiconductor switch section (OFF side) via the potential transmissionsection, and a low potential applied to the control terminal istransmitted.

[0036] As the second effect, the control voltage is much lower than theinput voltage in a high frequency semiconductor switch section (OFFside) on a path which cuts off a high frequency signal, and the OFFhandling power can be increased. This is because high frequencysemiconductor switch sections are isolated from each other in the DCstate, the input side or output side of the high frequency semiconductorswitch section (OFF side) is connected to the control terminal of theother high frequency semiconductor switch section (ON side) via thepotential transmission section, and a high potential applied to thecontrol terminal is transmitted.

[0037] A conventional circuit arrangement cannot attain these twoeffects at the same time. To the contrary, the present invention canachieve these two effects at the same time by, e.g., isolating highfrequency semiconductor switch sections in the DC state. As for a highfrequency semiconductor switch section which is opened upon applicationof a high potential to the switching signal terminal and closed uponapplication of a low potential, the voltage level in the abovedescription is reversed.

[0038] Other objects, aspects, and advantages of the present inventionwill be apparent to those skilled in the art from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich preferred examples complying with the principle of the presentinvention are described as embodiments.

BRIEF DESCRIPTION OF DRAWINGS

[0039]FIG. 1 is a circuit diagram showing the first prior art of a highfrequency switch circuit;

[0040]FIG. 2 is a circuit diagram showing the second prior art of a highfrequency switch circuit;

[0041]FIG. 3 is a circuit diagram showing the first embodiment of a highfrequency switch circuit according to the present invention;

[0042]FIGS. 4A to 4E are circuit diagrams showing the first to fifthexamples of a DC potential isolating section in the high frequencyswitch circuit according to the first embodiment, respectively;

[0043]FIGS. 5A and 5B are circuit diagrams showing examples of a highfrequency semiconductor switch section in the high frequency switchcircuit according to the first embodiment, respectively;

[0044]FIGS. 6A and 6B are circuit diagrams showing the first and secondexamples of a potential transmission section in the high frequencyswitch circuit according to the first embodiment, respectively;

[0045]FIG. 7 is a circuit diagram showing the second embodiment of ahigh frequency switch circuit according to the present invention;

[0046]FIG. 8 is a circuit diagram showing the third embodiment of a highfrequency switch circuit according to the present invention;

[0047]FIG. 9 is a circuit diagram showing the fourth embodiment of ahigh frequency switch circuit according to the present invention;

[0048]FIGS. 10A to 10D are circuit diagrams showing the first example ofthe first to fourth DC potential isolating sections in the highfrequency switch circuit according to the fourth embodiment,respectively;

[0049]FIGS. 11A to 11D are circuit diagrams showing the second exampleof the first to fourth DC potential isolating sections in the highfrequency switch circuit according to the fourth embodiment,respectively;

[0050]FIGS. 12A to 12D are circuit diagrams showing the third example ofthe first to fourth DC potential isolating sections in the highfrequency switch circuit according to the fourth embodiment,respectively;

[0051]FIGS. 13A to 13D are circuit diagrams showing the fourth exampleof the first to fourth DC potential isolating sections in the highfrequency switch circuit according to the fourth embodiment,respectively;

[0052]FIGS. 14A to 14D are circuit diagrams showing the fifth example ofthe first to fourth DC potential isolating sections in the highfrequency switch circuit according to the fourth embodiment,respectively;

[0053]FIG. 15 is a circuit diagram showing the fifth embodiment of ahigh frequency switch circuit according to the present invention;

[0054]FIG. 16 is a circuit diagram showing the sixth embodiment of ahigh frequency switch circuit according to the present invention;

[0055]FIG. 17 is a circuit diagram showing the seventh embodiment of ahigh frequency switch circuit according to the present invention; and

[0056]FIG. 18 is a circuit diagram showing the eighth embodiment of ahigh frequency switch circuit according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0057]FIG. 3 is a circuit diagram showing the first embodiment of a highfrequency switch circuit according to the present invention. The firstembodiment will be explained with FIG. 3.

[0058] The high frequency switch circuit according to the firstembodiment comprises high frequency terminals 101, 102, and 103 whichinput/output a high frequency signal, a high frequency semiconductorswitch section 121 which switches between the high frequency terminals101 and 102, a high frequency semiconductor switch section 122 whichswitches between the high frequency terminals 101 and 103, a switchingsignal terminal 111 which controls switching operation of the highfrequency semiconductor switch section 121, a switching signal terminal112 which controls switching operation of the high frequencysemiconductor switch section 122, a DC potential isolating section 131which is connected between the high frequency terminal 101 and the highfrequency semiconductor switch sections 121 and 122 and isolates thehigh frequency semiconductor switch sections 121 and 122 in the DCstate, a potential transmission section 141 which is connected betweenthe switching signal terminal 112 and the high frequency terminal 102and applies to the high frequency terminal 102 a DC potential applied tothe switching signal terminal 112, and a potential transmission section142 which is connected between the switching signal terminal 111 and thehigh frequency terminal 103 and applies to the high frequency terminal103 a DC potential applied to the switching signal terminal 111.

[0059]FIG. 3 illustrates arrows in the blocks of the high frequencysemiconductor switch sections 121 and 122. The proximal side of eacharrow represents the input side of a high frequency signal, and thedistal side represents the output side of the high frequency signal.

[0060] In the high frequency switch circuit according to the firstembodiment, the output side of the high frequency semiconductor switchsection 121 is connected to the high frequency terminal 102. The outputside of the high frequency semiconductor switch section 122 is connectedto the high frequency terminal 103. The input sides of the highfrequency semiconductor switch sections 121 and 122 are connected to thehigh frequency terminal 101 via the DC potential isolating section 131so as to prevent DC potentials at their input and output sides frombeing equal to each other. The control side of the high frequencysemiconductor switch section 121 is connected to the switching signalterminal 111. The control side of the high frequency semiconductorswitch section 122 is connected to the switching signal terminal 112.The potential transmission section 142 is connected to the switchingsignal terminal 111 in order to transmit to the high frequency terminal103 a voltage applied to the switching signal terminal 111. Thepotential transmission section 141 is connected to the switching signalterminal 112 in order to transmit to the high frequency terminal 102 avoltage applied to the switching signal terminal 112.

[0061]FIGS. 4A to 4C are circuit diagrams showing the first to thirdexamples of the DC potential isolating section in the high frequencyswitch circuit according to the first embodiment. The first to thirdexamples will be explained with reference to FIGS. 3 and 4A to 4C.

[0062] As shown in FIG. 4A, a DC potential isolating section 131 ₁ inthe first example is comprised of a capacitive element 41 connectedbetween the high frequency terminal 101 and the input side of the highfrequency semiconductor switch section 121, and a capacitive element 42connected between the high frequency terminal 101 and the input side ofthe high frequency semiconductor switch section 122. As shown in FIG.4B, a DC potential isolating section 131 ₂ in the second example iscomprised of a capacitive element 42 connected between the highfrequency terminal 101 and the input side of the high frequencysemiconductor switch section 122. As shown in FIG. 4C, a DC potentialisolating section 131 ₃ in the third example is comprised of acapacitive element 41 connected between the high frequency terminal 101and the input side of the high frequency semiconductor switch section121.

[0063]FIGS. 4D and 4E are circuit diagrams showing the fourth and fifthexamples of the DC potential isolating section in the high frequencyswitch circuit according to the first embodiment. The fourth and fifthexamples will be explained with reference to FIGS. 3, 4D, and 4E.

[0064] As shown in FIG. 4D, a DC potential isolating section 131 ₄ inthe fourth example comprises a field effect transistor 1 having drainand source electrodes connected between the high frequency terminal 101and the high frequency semiconductor switch section 121, a field effecttransistor 2 having drain and source electrodes connected between thehigh frequency terminal 101 and the high frequency semiconductor switchsection 122, a resistance element 51 connected between the gateelectrode of the field effect transistor 1 and the switching signalterminal 111, and a resistance element 52 connected between the gateelectrode of the field effect transistor 2 and the switching signalterminal 112.

[0065] As shown in FIG. 4E, a DC potential isolating section 131 ₅ inthe fifth example comprises a resistance element 53 connected betweenthe drain and source electrodes of the field effect transistor 1, and aresistance element 54 connected between the drain and source electrodesof the field effect transistor 2, in addition to the arrangement of theDC potential isolating section in the fourth example. The resistanceelements 53 and 54 have a high resistance value of, e.g., several tenkΩ.

[0066]FIGS. 5A and 5B are circuit diagrams showing the first and secondexamples of the high frequency semiconductor switch section in the highfrequency switch circuit according to the first embodiment. The firstand second examples will be explained with reference to FIGS. 3, 5A, and5B.

[0067] As shown in FIG. 5A, a high frequency semiconductor switchsection 121 ₁ in the first example comprises a field effect transistor 1having drain and source electrodes connected between the high frequencyterminals 101 and 102, a resistance element 52 connected between thegate electrode of the field effect transistor 1 and the switching signalterminal 111, and a resistance element 51 connected between the drainand source electrodes of the field effect transistor 1. The resistanceelement 51 is arranged to set potentials at the drain and source of thefield effect transistor 1 equal to each other, and has a resistancevalue of, e.g., several kΩ or higher.

[0068] As shown in FIG. 5B, a high frequency semiconductor switchsection 121 ₂ in the second example comprises field effect transistors1, 2, and 3 having drain and source electrodes series-connected betweenthe high frequency terminals 101 and 102, resistance elements 54, 55,and 56 respectively connected between the gate electrodes of the fieldeffect transistors 1, 2, and 3 and the switching signal terminal 111,and resistance elements 51, 52, and 53 respectively connected betweenthe drain and source electrodes of the field effect transistors 1, 2,and 3. The resistance elements 51 to 53 are arranged to set potentialsat the drains and sources of the field effect transistors 1 to 3 equalto each other, and have a resistance value of, e.g., several kΩ orhigher.

[0069] The high frequency semiconductor switch section 122 in FIG. 3also complies with the arrangements of the high frequency semiconductorswitch sections 121 ₁ and 121 ₂ in FIGS. 5A and 5B. A single or threefield effect transistors are connected in FIGS. 5A and 5B, but two orfour or more field effect transistors may be connected.

[0070]FIGS. 6A and 6B are circuit diagrams showing the first and secondexamples of the potential transmission section in the high frequencyswitch circuit according to the first embodiment. The first and secondexamples will be explained with reference to FIGS. 3, 6A, and 6B.

[0071] As shown in FIG. 6A, a potential transmission section 141 in thefirst example comprises a resistance element 51. The resistance element51 has a resistance value of, e.g., several ten kΩ or higher. As shownin FIG. 6B, a potential transmission section 141 ₂ in the second examplecomprises a resistance element 51 and inductor element 91 which areseries-connected to each other.

[0072] The potential transmission section 142 in FIG. 3 also complieswith the arrangements of the potential transmission sections 141 ₁ and141 ₂ in FIGS. 6A and 6B. The potential transmission section 141 isconnected to only the output side of the high frequency semiconductorswitch section 121 in FIG. 3, but may be connected to only the inputside of the high frequency semiconductor switch section 121 or both theinput and output sides of the high frequency semiconductor switchsection 121. Similarly, the potential transmission section 142 isconnected to only the output side of the high frequency semiconductorswitch section 122 in FIG. 3, but may be connected to only the inputside of the high frequency semiconductor switch section 122 or both theinput and output sides of the high frequency semiconductor switchsection 122.

[0073] The operation of the high frequency switch circuit according tothe first embodiment will be described with reference to FIG. 3.

[0074] Assume that high level is input to the switching signal terminal111, and low level is input to the switching signal terminal 112. Atthis time, the input and output sides of the high frequencysemiconductor switch section 121 are connected to the switching signalterminal 112 via the potential transmission section 141, and thepotential drops close to low level. The potential on the control side ofthe high frequency semiconductor switch section 121 becomes much higherthan the potentials on the input and output sides. This sufficientlydecreases the ON resistance of the high frequency semiconductor switchsection 121, reducing the transmission loss.

[0075] In the DC state, the input and output sides of the high frequencysemiconductor switch section 122 are disconnected from the input andoutput sides of the high frequency semiconductor switch section 121 bythe DC potential isolating section 131. The input and output sides ofthe high frequency semiconductor switch section 122 can take valuesdifferent from the potentials on the input and output sides of the highfrequency semiconductor switch section 121. That is, the input andoutput sides of the high frequency semiconductor switch section 122 areconnected to the switching signal terminal 111 via the potentialtransmission section 142, and the potential rises close to high level.The potential on the control side of the high frequency semiconductorswitch section 122 becomes much lower than the potentials on the inputand output sides of the high frequency semiconductor switch section 122.The high frequency semiconductor switch section 122 is therefore turnedoff. The input and output sides of the high frequency semiconductorswitch section 122 become higher in potential than the input and outputsides of the high frequency semiconductor switch section 121.

[0076] Letting Vn be the potential on the input and output sides of thehigh frequency semiconductor switch section 122, VL be low level, and VTbe the threshold voltage of the field effect transistor whichconstitutes the high frequency semiconductor switch section 122, maximumpower Pmax capable of maintaining the OFF state is given by

Pmax=2{n(Vn−VL+VT)}2/Zo

[0077] (where n is the number of cascade connection stages of fieldeffect transistors which constitute the high frequency semiconductorswitch section 122, and Zo is the evaluation system impedance in theswitch circuit.)

[0078] In the first embodiment, Vn can be set high. As is apparent fromthe above equation, Pmax becomes higher than that in a case wherein thehigh frequency semiconductor switch sections 121 and 122 are notisolated in the DC state. Reduction in transmission loss and an increasein handling power can be simultaneously achieved.

[0079]FIG. 7 is a circuit diagram showing the second embodiment of ahigh frequency switch circuit according to the present invention. Thesecond embodiment will be explained with reference to FIG. 7.

[0080] In the high frequency switch circuit according to the secondembodiment, DC potential isolating sections 131 and 132 adopt thearrangement shown in FIG. 4D, high frequency semiconductor switchsections 121 and 122 adopt the arrangement shown in FIG. 5B, andpotential transmission sections 141 and 142 adopt the arrangement shownin FIG. 6A. The high frequency switch circuit according to the secondembodiment exhibits the same operations and effects as those of the highfrequency switch circuit according to the first embodiment.

[0081]FIG. 8 is a circuit diagram showing the third embodiment of a highfrequency switch circuit according to the present invention. The thirdembodiment will be explained with reference to FIG. 8.

[0082] In the high frequency switch circuit according to the thirdembodiment, DC potential isolating sections 131 and 132 adopt thearrangement shown in FIG. 4E, high frequency semiconductor switchsections 121 and 122 adopt the arrangement shown in FIG. 5B, andpotential transmission sections 141 and 142 adopt the arrangement shownin FIG. 6A. The high frequency switch circuit according to the thirdembodiment exhibits the same operations and effects as those of the highfrequency switch circuit according to the first embodiment.

[0083]FIG. 9 is a circuit diagram showing the fourth embodiment of ahigh frequency switch circuit according to the present invention. Thefourth embodiment will be explained with FIG. 9.

[0084] The high frequency switch circuit according to the fourthembodiment comprises high frequency terminals 101 to 104 whichinput/output a high frequency signal, a high frequency switch section121 which switches between the high frequency terminals 101 and 102, ahigh frequency switch section 122 which switches between the highfrequency terminals 102 and 103, a high frequency semiconductor switchsection 123 which switches between the high frequency terminals 103 and104, a high frequency semiconductor switch section 124 which switchesbetween the high frequency terminals 104 and 101, a switching signalterminal 111 which controls switching operation of the high frequencysemiconductor switch sections 121 and 123, a switching signal terminal112 which controls switching operation of the high frequencysemiconductor switch sections 122 and 124, a DC potential isolatingsection 131 which is connected between the high frequency terminal 131and the high frequency semiconductor switch sections 124 and 121 andisolates the high frequency semiconductor switch section 124 and thehigh frequency switch section 121 in the DC state, a DC potentialisolating section 132 which is connected between the high frequencyterminal 102 and the high frequency semiconductor switch sections 121and 122 and isolates the high frequency semiconductor switch sections121 and 122 in the DC state, a DC potential isolating section 133 whichis connected between the high frequency terminal 103 and the highfrequency semiconductor switch sections 122 and 123 and isolates thehigh frequency semiconductor switch sections 122 and 123 in the DCstate, a DC potential isolating section 134 which is connected betweenthe high frequency terminal 104 and the high frequency semiconductorswitch sections 123 and 124 and isolates the high frequencysemiconductor switch sections 123 and 124 in the DC state, a potentialtransmission section 141 which is connected between the switching signalterminal 112 and the input side of the high frequency semiconductorswitch section 121 and applies to the input side a DC potential appliedto the switching signal terminal 112, a potential transmission section142 which is connected between the switching signal terminal 112 and theoutput side of the high frequency semiconductor switch section 121 andapplies to the output side a DC potential applied to the switchingsignal terminal 112, a potential transmission section 143 which isconnected between the switching signal terminal 111 and the input sideof the high frequency semiconductor switch section 122 and applies tothe input side a DC potential applied to the switching signal terminal111, a potential transmission section 144 which is connected between theswitching signal terminal 111 and the output side of the high frequencysemiconductor switch section 122 and applies to the output side a DCpotential applied to the switching signal terminal 111, a potentialtransmission section 145 which is connected between the switching signalterminal 112 and the input side of the high frequency semiconductorswitch section 123 and applies to the input side a DC potential appliedto the switching signal terminal 112, a potential transmission section146 which is connected between the switching signal terminal 112 and theoutput side of the high frequency semiconductor switch section 123 andapplies to the output side a DC potential applied to the switchingsignal terminal 112, a potential transmission section 147 which isconnected between the switching signal terminal 111 and the input sideof the high frequency semiconductor switch section 124 and applies tothe input side a DC potential applied to the switching signal terminal111, and a potential transmission section 148 which is connected betweenthe switching signal terminal 111 and the output side of the highfrequency semiconductor switch section 124 and applies to the outputside a DC potential applied to the switching signal terminal 111.

[0085]FIG. 9 illustrates arrows in the blocks of the high frequencysemiconductor switch sections 121 to 124. The proximal side of eacharrow represents the input side of a high frequency signal, and thedistal side represents the output side of the high frequency signal.

[0086] In the high frequency switch circuit according to the fourthembodiment, the high frequency terminal 101 is connected to the DCpotential isolating section 131, the high frequency terminal 102 isconnected to the DC potential isolating section 132, the high frequencyterminal 103 is connected to the DC potential isolating section 133, andthe high frequency terminal 104 is connected to the DC potentialisolating section 134. Of the high frequency semiconductor switchsections 121 to 124, the input side of the high frequency semiconductorswitch section 121 is connected to the DC potential isolating section131, and the output side of the section 121 is connected to the DCpotential isolating section 132. The input side of the high frequencysemiconductor switch section 122 is connected to the DC potentialisolating section 132, and the output side of the section 122 isconnected to the DC potential isolating section 133. The input side ofthe high frequency semiconductor switch section 123 is connected to theDC potential isolating section 133, and the output side of the section123 is connected to the DC potential isolating section 134. The inputside of the high frequency semiconductor switch section 124 is connectedto the DC potential isolating section 134, and the output side of thesection 124 is connected to the DC potential isolating section 131. Thecontrol sides of the high frequency switches 121 and 123 are connectedto the switching signal terminal 111, and the control sides of the highfrequency switches 122 and 124 are connected to the switching signalterminal 112. In order to transmit a control voltage input to theswitching signal terminal 111 to the high frequency semiconductor switchsections 122 and 124, the potential transmission section 143 isconnected to the input side of the high frequency semiconductor switchsection 122, the potential transmission section 144 is connected to theoutput side of the high frequency semiconductor switch section 122, thepotential transmission section 147 is connected to the input side of thehigh frequency semiconductor switch section 124, and the potentialtransmission section 148 is connected to the output side of the highfrequency semiconductor switch section 124. In order to transmit acontrol voltage input to the switching signal terminal 112 to the highfrequency semiconductor switch sections 121 and 123, the potentialtransmission section 141 is connected to the input side of the highfrequency semiconductor switch section 121, the potential transmissionsection 142 is connected to the output side of the high frequencysemiconductor switch section 121, the potential transmission section 145is connected to the input side of the high frequency semiconductorswitch section 123, and the potential transmission section 146 isconnected to the output side of the high frequency semiconductor switchsection 123.

[0087]FIGS. 10A to 10D are circuit diagrams showing the first example ofthe DC potential isolating section in the high frequency switch circuitaccording to the fourth embodiment. The first example will be explainedwith reference to FIGS. 9 and 10A to 10D.

[0088] As shown in FIGS. 10A to 10D, a DC potential isolating section131 a is comprised of a capacitive element 48 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 124, and a capacitive element 41 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 121. A DC potential isolating section 132a is comprised of acapacitive element 42 connected between the high frequency terminal 102and the high frequency semiconductor switch section 121, and acapacitive element 43 connected between the high frequency terminal 102and the high frequency semiconductor switch section 122. A DC potentialisolating section 133 a is comprised of a capacitive element 44connected between the high frequency terminal 103 and the high frequencysemiconductor switch section 122, and a capacitive element 45 connectedbetween the high frequency terminal 101 and the high frequencysemiconductor switch section 123. A DC potential isolating section 134 ais comprised of a capacitive element 46 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 123, and a capacitive element 47 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 124.

[0089]FIGS. 11A to 11D are circuit diagrams showing the second exampleof the DC potential isolating section in the high frequency switchcircuit according to the fourth embodiment. The second example will beexplained with reference to FIGS. 9 and 11A to 11D.

[0090] As shown in FIGS. 11A to 11D, a DC potential isolating section131 b is comprised of a capacitive element 41 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 121. A DC potential isolating section 132 b is comprised of acapacitive element 42 connected between the high frequency terminal 102and the high frequency semiconductor switch section 121. A DC potentialisolating section 133 b is comprised of a capacitive element 45connected between the high frequency terminal 101 and the high frequencysemiconductor switch section 123. A DC potential isolating section 134 bis comprised of a capacitive element 46 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 123.

[0091]FIGS. 12A to 12D are circuit diagrams showing the third example ofthe DC potential isolating section in the high frequency switch circuitaccording to the fourth embodiment. The third example will be explainedwith reference to FIGS. 9 and 12A to 12D.

[0092] As shown in FIGS. 12A to 12D, a DC potential isolating section131c is comprised of a capacitive element 41 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 121. A DC potential isolating section 132 c is comprised of acapacitive element 43 connected between the high frequency terminal 102and the high frequency semiconductor switch section 122. A DC potentialisolating section 133 c is comprised of a capacitive element 45connected between the high frequency terminal 101 and the high frequencysemiconductor switch section 123. A DC potential isolating section 134 cis comprised of a capacitive element 47 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 124.

[0093]FIGS. 13A to 13D are circuit diagrams showing the fourth exampleof the DC potential isolating section in the high frequency switchcircuit according to the fourth embodiment. The fourth example will beexplained with reference to FIGS. 9 and 13A to 13D.

[0094] As shown in FIGS. 13A to 13D, a DC potential isolating section131 d is comprised of a capacitive element 41 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 121. A DC potential isolating section 132 d is comprised of acapacitive element 42 connected between the high frequency terminal 102and the high frequency semiconductor switch section 121. A DC potentialisolating section 133 d is comprised of a capacitive element 44connected between the high frequency terminal 103 and the high frequencysemiconductor switch section 122. A DC potential isolating section 134 dis comprised of a capacitive element 46 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 123.

[0095]FIGS. 14A to 14D are circuit diagrams showing the fifth example ofthe DC potential isolating section in the high frequency switch circuitaccording to the fourth embodiment. The fifth example will be explainedwith reference to FIGS. 9 and 14A to 14D.

[0096] As shown in FIGS. 14A to 14D, a DC potential isolating section131 e is comprised of a capacitive element 41 connected between the highfrequency terminal 101 and the high frequency semiconductor switchsection 121. A DC potential isolating section 132 e is comprised of acapacitive element 43 connected between the high frequency terminal 102and the high frequency semiconductor switch section 122. A DC potentialisolating section 133 e is comprised of a capacitive element 44connected between the high frequency terminal 103 and the high frequencysemiconductor switch section 122. A DC potential isolating section 134 eis comprised of a capacitive element 46 connected between the highfrequency terminal 104 and the high frequency semiconductor switchsection 123.

[0097] The DC potential isolating sections 131 to 134 in the highfrequency switch circuit according to the fourth embodiment may adoptthe arrangements shown in FIGS. 4D and 4E. The high frequencysemiconductor switch sections 121 to 124 in the high frequency switchcircuit according to the fourth embodiment may adopt the arrangementsshown in FIGS. 5A and 5B. The potential transmission sections 141 to 148in the high frequency switch circuit according to the fourth embodimentmay adopt the arrangements shown in FIGS. 6A and 6B. The high frequencyswitch circuit according to the fourth embodiment exhibits the sameoperations and effects as those of the high frequency switch circuitaccording to the first embodiment.

[0098]FIG. 15 is a circuit diagram showing the fifth embodiment of ahigh frequency switch circuit according to the present invention. Thefifth embodiment will be explained with reference to FIG. 15.

[0099] The high frequency switch circuit according to the fifthembodiment is different from the fourth embodiment in that this highfrequency switch circuit comprises a potential transmission section 141which is connected between a switching signal terminal 112 and the inputside of a high frequency semiconductor switch section 121 and applies tothe input side a DC potential applied to the switching signal terminal112, a potential transmission section 142 which is connected between aswitching signal terminal 111 and the input side of a high frequencysemiconductor switch section 122 and applies to the input side a DCpotential applied to the switching signal terminal 111, a potentialtransmission section 143 which is connected between the switching signalterminal 112 and the input side of a high frequency semiconductor switchsection 123 and applies to the input side a DC potential applied to theswitching signal terminal 112, and a potential transmission section 144which is connected between the switching signal terminal 111 and theinput side of a high frequency semiconductor switch section 124 andapplies to the input side a DC potential applied to the switching signalterminal 111.

[0100] DC potential isolating sections 131 to 134 in the high frequencyswitch circuit according to the fifth embodiment may adopt thearrangements shown in FIGS. 10A to 14D, 4D, and 4E. The high frequencysemiconductor switch sections 121 to 124 in the high frequency switchcircuit according to the fifth embodiment may adopt the arrangementsshown in FIGS. 5A and 5B. The potential transmission sections 141 to 144in the high frequency switch circuit according to the fifth embodimentmay adopt the arrangements shown in FIGS. 6A and 6B. The high frequencyswitch circuit according to the fifth embodiment exhibits the sameoperations and effects as those of the high frequency switch circuitaccording to the fourth embodiment.

[0101]FIG. 16 is a circuit diagram showing the sixth embodiment of ahigh frequency switch circuit according to the present invention. Thesixth embodiment will be explained with reference to FIG. 16.

[0102] The high frequency switch circuit according to the sixthembodiment is different from the fourth embodiment in that this highfrequency switch circuit comprises a potential transmission section 141which is connected between a switching signal terminal 112 and the inputside of a high frequency switch section 121 and applies to the inputside a DC potential applied to the switching signal terminal 112, apotential transmission section 142 which is connected between aswitching signal terminal 111 and the input side of a high frequencysemiconductor switch section 122 and applies to the input side a DCpotential applied to the switching signal terminal 111, a potentialtransmission section 143 which is connected between the switching signalterminal 112 and the output side of a high frequency semiconductorswitch section 123 and applies to the output side a DC potential appliedto the switching signal terminal 112, and a potential transmissionsection 148 which is connected between the switching signal terminal 111and the output side of a high frequency semiconductor switch section 124and applies to the output side a DC potential applied to the switchingsignal terminal 111.

[0103] DC potential isolating sections 131 to 134 in the high frequencyswitch circuit according to the sixth embodiment may adopt thearrangements shown in FIGS. 10A to 14D, 4D, and 4E. The high frequencysemiconductor switch sections 121 to 124 in the high frequency switchcircuit according to the sixth embodiment may adopt the arrangementsshown in FIGS. 5A and 5B. The potential transmission sections 141 to 144in the high frequency switch circuit according to the sixth embodimentmay adopt the arrangements shown in FIGS. 6A and 6B. The high frequencyswitch circuit according to the sixth embodiment exhibits the sameoperations and effects as those of the high frequency switch circuitaccording to the fourth embodiment.

[0104]FIG. 17 is a circuit diagram showing the seventh embodiment of ahigh frequency switch circuit according to the present invention. Theseventh embodiment will be explained with reference to FIG. 17.

[0105] In the high frequency switch circuit according to the seventhembodiment, DC potential isolating sections 131 to 134 adopt thearrangement shown in FIG. 4D, high frequency semiconductor switchsections 121 to 124 adopt the arrangement shown in FIG. 5B, andpotential transmission sections 141 to 144 adopt the arrangement shownin FIG. 6A. The high frequency switch circuit according to the seventhembodiment exhibits the same operations and effects as those of the highfrequency switch circuit according to the fourth embodiment.

[0106]FIG. 18 is a circuit diagram showing the eighth embodiment of ahigh frequency switch circuit according to the present invention. Theeighth embodiment will be explained with reference to FIG. 18.

[0107] In the high frequency switch circuit according to the eighthembodiment, DC potential isolating sections 131 to 134 adopt thearrangement shown in FIG. 4E, high frequency semiconductor switchsections 121 to 124 adopt the arrangement shown in FIG. 5B, andpotential transmission sections 141 to 144 adopt the arrangement shownin FIG. 6A. The high frequency switch circuit according to the eighthembodiment exhibits the same operations and effects as those of the highfrequency switch circuit according to the fourth embodiment.

1. A high frequency switch circuit characterized by comprising aplurality of high frequency terminals which input/output a highfrequency signal, and a plurality of high frequency semiconductor switchsections which are arranged on lines coupling said high frequencyterminals, wherein said plurality of high frequency semiconductor switchsections are isolated from each other in a DC state, and a DC potentialopposite in level to a DC potential applied to a control side is appliedto at least one of an input side and an output side of each of saidplurality of high frequency semiconductor switch sections by using aswitching control voltage without using an external power supply.
 2. Ahigh frequency switch circuit according to claim 1, characterized inthat each of said plurality of high frequency semiconductor switchsections includes a field effect transistor having a drain electrode anda source electrode which are connected between said high frequencyterminals, said plurality of high frequency semiconductor switchsections are isolated from each other by capacitive elements of, and aDC potential opposite in level to a DC potential applied to a gateelectrode is applied to at least one of the drain electrode and thesource electrode by using a switching control voltage without using anexternal power supply.
 3. A high frequency switch circuit according toclaim 1, characterized in that each of said plurality of high frequencysemiconductor switch sections includes a plurality of field effecttransistors having drain electrodes and source electrodes which areseries-connected between said high frequency terminals, said pluralityof high frequency semiconductor switch sections are isolated from eachother by capacitive elements of, and a DC potential opposite in level toa DC potential applied to gate electrodes is applied to at least eitherof the drain electrodes and the source electrodes at both sides of saidplurality of field effect transistors by using a switching controlvoltage without using an external power supply.
 4. A high frequencyswitch circuit comprising: first to third high frequency terminals whichinput/output a high frequency signal; a first high frequencysemiconductor switch section which switches between said third highfrequency terminal and said first high frequency terminal; a second highfrequency semiconductor switch section which switches between said thirdhigh frequency terminal and said second high frequency terminal; a firstswitching signal terminal which controls switching operation of saidfirst high frequency semiconductor switch section; a second switchingsignal terminal which controls switching operation of said second highfrequency semiconductor switch section; a DC potential isolating sectionwhich is connected between said third high frequency terminal and saidfirst and second high frequency semiconductor switch sections, andisolates said first high frequency semiconductor switch section and saidsecond high frequency semiconductor switch section in a DC state; afirst potential transmission section which is connected between saidsecond switching signal terminal and said first high frequency terminal,and applies to said first high frequency terminal a DC potential appliedto said second switching signal terminal; and a second potentialtransmission section which is connected between said first switchingsignal terminal and said second high frequency terminal, and applies tosaid second high frequency terminal a DC potential applied to said firstswitching signal terminal.
 5. A high frequency switch circuitcomprising: first to fourth high frequency terminals which input/outputa high frequency signal; a first high frequency semiconductor switchsection which switches between said first high frequency terminal andsaid second high frequency terminal; a second high frequencysemiconductor switch section which switches between said second highfrequency terminal and said third high frequency terminal; a third highfrequency semiconductor switch section which switches between said thirdhigh frequency terminal and said fourth high frequency terminal; afourth high frequency semiconductor switch section which switchesbetween said fourth high frequency terminal and said first highfrequency terminal; a first switching signal terminal which controlsswitching operation of said first and third high frequency semiconductorswitch sections; a second switching signal terminal which controlsswitching operation of said second and fourth high frequencysemiconductor switch sections; a first DC potential isolating sectionwhich is connected between said first high frequency terminal and saidfourth and first high frequency semiconductor switch sections, andisolates said fourth high frequency semiconductor switch section andsaid first high frequency semiconductor switch section in a DC state; asecond DC potential isolating section which is connected between saidsecond high frequency terminal and said first and second high frequencysemiconductor switch sections, and isolates said first high frequencysemiconductor switch section and said second high frequencysemiconductor switch section in the DC state; a third DC potentialisolating section which is connected between said third high frequencyterminal and said second and third high frequency semiconductor switchsections, and isolates said second high frequency semiconductor switchsection and said third high frequency semiconductor switch section inthe DC state; a fourth DC potential isolating section which is connectedbetween said fourth high frequency terminal and said third and fourthhigh frequency semiconductor switch sections, and isolates said thirdhigh frequency semiconductor switch section and said fourth highfrequency semiconductor switch section in the DC state; a firstpotential transmission section which is connected between said secondswitching signal terminal and at least one of an input side and anoutput side of said first high frequency semiconductor switch section,and applies to said at least one of the input side and the output side aDC potential applied to said second switching signal terminal; a secondpotential transmission section which is connected between said firstswitching signal terminal and at least one of an input side and anoutput side of said second high frequency semiconductor switch section,and applies to said at least one of the input side and the output side aDC potential applied to said first switching signal terminal; a thirdpotential transmission section which is connected between said secondswitching signal terminal and at least one of an input side and anoutput side of said third high frequency semiconductor switch section,and applies to said at least one of the input side and the output side aDC potential applied to said second switching signal terminal; and afourth potential transmission section which is connected between saidfirst switching signal terminal and at least one of an input side and anoutput side of said fourth high frequency semiconductor switch section,and applies to said at least one of the input side and the output side aDC potential applied to said first switching signal terminal.
 6. A highfrequency switch circuit according to any one of claims 4 and 5,characterized in that said DC potential isolating section includes acapacitive element which is connected between said high frequencyterminal connected to said DC potential isolating section and one highfrequency semiconductor switch section connected to said DC potentialisolating section, or between said high frequency terminal connected tosaid DC potential isolating section and the other high frequencysemiconductor switch section connected to said DC potential isolatingsection.
 7. A high frequency switch circuit according to any one ofclaims 4, 5, and 6, characterized in that said DC potential isolatingsection comprises a field effect transistor having a drain electrode anda source electrode which are connected between said high frequencyterminal connected to said DC potential isolating section and one highfrequency semiconductor switch section connected to said DC potentialisolating section, a field effect transistor having a drain electrodeand a source electrode which are connected between said high frequencyterminal connected to said DC potential isolating section and the otherhigh frequency semiconductor switch section connected to said DCpotential isolating section, and a resistance element which is connectedbetween a gate electrode of each field effect transistor and saidswitching signal terminal.
 8. A high frequency switch circuit accordingto any one of claims 4, 5, and 6, characterized in that said DCpotential isolating section comprises a field effect transistor having adrain electrode and a source electrode which are connected between saidhigh frequency terminal connected to said DC potential isolating sectionand one high frequency semiconductor switch section connected to said DCpotential isolating section, a field effect transistor having a drainelectrode and a source electrode which are connected between said highfrequency terminal connected to said DC potential isolating section andthe other high frequency semiconductor switch section connected to saidDC potential isolating section, a resistance element which is connectedbetween a gate electrode of each field effect transistor and saidswitching signal terminal, and a resistance element which is connectedbetween the drain electrode and the source electrode of each fieldeffect transistor.
 9. A high frequency switch circuit according to anyone of claims 4 to 8, characterized in that said high frequencysemiconductor switch section comprises a field effect transistor havinga drain electrode and a source electrode which are connected betweensaid high frequency terminals connected/disconnected by said highfrequency semiconductor switch section, a resistance element which isconnected between a gate electrode of the field effect transistor andsaid switching signal terminal for controlling said high frequencysemiconductor switch section, and a resistance element which isconnected between the drain electrode and the source electrode.
 10. Ahigh frequency switch circuit according to any one of claims 4 to 8,characterized in that said high frequency semiconductor switch sectioncomprises a plurality of field effect transistors having drainelectrodes and source electrodes which are series-connected between saidhigh frequency terminals connected/disconnected by said high frequencysemiconductor switch sections, a plurality of resistance elements whichare connected between gate electrodes of the field effect transistorsand said switching signal terminals for controlling said high frequencysemiconductor switch sections, and a plurality of resistance elementswhich are connected between the drain electrodes and the sourceelectrodes.
 11. A high frequency switch circuit according to any one ofclaims 4 to 10, characterized in that said potential transmissionsection includes a resistance element.
 12. A high frequency switchcircuit according to any one of claims 4 to 10, characterized in thatsaid potential transmission section includes a resistance element and aninductor element which are series-connected.
 13. A high frequency switchcircuit according to any one of claims 1 to 12, characterized in thatsaid high frequency switch circuit is integrated in one semiconductorchip.
 14. (added) A high frequency switch circuit according to claim 1,characterized in that, of said plurality of high frequency semiconductorswitch sections, at least one of an input side and an output side of aswitch section which is closed receives a DC potential which sets anopen state upon application to a control side of said switch section,and of said plurality of high frequency semiconductor switch sections,at least one of an input side and an output side of a switch sectionwhich is opened receives a DC potential which sets a closed state uponapplication to a control side of said switch section.
 15. (added) A highfrequency switch circuit according to claim 14, characterized in thatthe DC potential applied to the control side is branched and applied toat least one of said switch section which is closed, and the DCpotential applied to the control side is branched and applied to atleast one of said switch section which is opened.